Hemophilus infections, most of which are due to Haemophilus influenzae infections, are a group of contagious diseases that are caused by a bacterium and affect only humans. Some hemophilus infections are potentially fatal.
H. influenzae is a common organism worldwide; it has been found in the nasal secretions of as many as 90 percent of healthy individuals in the general population. Hemophilus infections are characterized by acute inflammation with a discharge (exudate). They may affect almost any organ system but are most common in the respiratory tract. The organism can be transmitted by person-to-person contact or by contact with nasal discharges and other body fluids. Hemophilus infections in the United States are most likely to spread in the late winter or early spring.
The primary factor influencing the rate of infection is age; children between the ages of six months and four years are most vulnerable to H. influenzae. In the twentieth century, about 50 percent of children would acquire a hemophilus infection before reaching one year of age; almost all children would develop one before age three. In the United States, these figures have declined, however, as a result of the increasing use of hemophilus vaccines for children. Worldwide, however, Haemophilus influenzae remains a significant childhood pathogen. It is the primary cause of childhood meningitis and the second most common cause of childhood pneumonia. In developing countries, Haemophilus influenzae is responsible for 500,000 annual deaths in children under the age of five.
Causes and symptoms
Hemophilus infections are primarily caused by Haemophilus influenzae, a bacterium that is capable of spreading from the nasal tissues and upper airway, where it is usually found, to the chest, throat, or middle ear. The organism sometimes invades localized areas of tissue, producing meningitis, infectious arthritis, conjunctivitis, cellulitis, epiglottitis, or inflammation of the membrane surrounding the heart. The most serious infections are caused by a strain called H. influenzae b (Hib). Before routine vaccination, Hib was the most common cause of bacterial meningitis and responsible for most of the cases of acquired mental retardation in the United States.
Bacterial sepsis in the newborn
Bacterial sepsis (the presence of illness-causing microorganisms, or their poisons, in the blood) is a potentially fatal illness in newborn infants. The child may acquire the disease organism as it passes through the mother's birth canal or from the hospital environment. H. influenzae can also produce inflammations of the eye (conjunctivitis) in newborn children. The signs of sepsis may include fever, fussiness, feeding problems, breathing difficulties, pale or mottled skin, or drowsiness. Premature birth is the most significant risk factor for hemophilus infections in newborns.
Epiglottitis is a potentially fatal hemophilus infection. Although children are more likely to develop epiglottitis, it can occur in adults as well. When the epiglottis (the flap that covers the trachea during swallowing so that food odes not enter the lungs) is infected, it can swell to the point where it blocks the windpipe. The symptoms of epiglottitis include a sudden high fever, drooling, the feeling of an object stuck in the throat, and stridor (a high-pitched, noisy respiratory sound). The epiglottis will look swollen and bright red if the doctor examines the patient's throat with a laryngoscope (a viewing device).
Meningitis caused by Hib is most common in children between nine months and four years of age. The child usually develops upper respiratory symptoms followed by fever, loss of appetite, vomiting, headache, and a stiff or sore neck or back. In severe cases, the child may have convulsions or go into shock or coma.
Hib is the second most common cause of middle ear infection and sinusitis in children. The symptoms of sinusitis include fever, pain, bad breath, and coughing. Children may also develop infectious arthritis from Hib. The joints most frequently affected are the large weight-bearing ones.
The diagnosis is usually based on a combination of the patient's symptoms and the results of blood counts, cultures, or antigen detection tests.
Laboratory tests can be used to confirm the diagnosis of hemophilus infections. The bacterium can be grown on chocolate agar or identified by blood cultures or Gram stain of body fluids. Antigen detection tests can be used to identify hemophilus infections in children. These tests include latex agglutination and electrophoresis.
Other laboratory findings that are associated with hemophilus infections include anemia (low red blood cell count) and a drop in the number of white blood cells in children with severe infections. Adults often show an abnormally high level of white blood cells; cell counts of 15,000 to 30,000/mm3 are not unusual.
Because some hemophilus infections are potentially fatal, treatment is started without waiting for the results of laboratory tests.
Hemophilus infections are treated with antibiotics. Patients who are severely ill are given ampicillin or a third-generation cephalosporin, such as cefotaxime or ceftriaxone, intravenously. Patients with milder infections are given oral antibiotics, including amoxicillin, cefaclor, erythromycin, or trimethoprim-sulfamethoxazole. Patients who are allergic to penicillin are usually given cefaclor or trimethoprim-sulfamethoxazole.
Patients with Hib strains that are resistant to ampicillin may be given chloramphenicol. Chloramphenicol is not a first-choice drug because of its side effects, including interference with bone marrow production of blood cells.
The duration of antibiotic treatment depends on the location and severity of the hemophilus infection. Adults with respiratory tract infections, or Hib pneumonia, are usually given a 10 to 14 day course of antibiotics. Meningitis is usually treated for 10 to 14 days, but a seven-day course of treatment with ceftriaxone appears to be sufficient for infants and children. Ear infections are treated for seven to 10 days.
Patients with serious hemophilus infections require bed rest and a humidified environment (such as a croup tent) if the respiratory tract is affected. Patients with epiglottitis frequently require intubation (insertion of a breathing tube) or a tracheotomy to keep the airway open. Patients with inflammation of the heart membrane, pneumonia, or arthritis may need surgical treatment to drain infected fluid from the chest cavity or inflamed joints.
Supportive care also includes monitoring of blood cell counts for patients using chloramphenicol, ampicillin, or other drugs that may affect production of blood cells by the bone marrow.
The most important factors in the prognosis are the severity of the infection and promptness of treatment. Untreated hemophilus infections—particularly meningitis, sepsis, and epiglottitis—have a high mortality rate. Bacterial sepsis of the newborn has a mortality rate of 13–50 percent. The prognosis is usually good for patients with mild infections who are treated without delay. Children who develop Hib arthritis sometimes have lasting problems with joint function.
There are three different vaccines for hemophilus infections used to immunize children in the United States: PRP-D, HBOC, and PRP-OMP. PRP-D is used only in children older than 15 months. HBOC is administered to infants at two, four, and six months after birth, with a booster dose at 15 to 18 months. PRP-OMP is administered to infants at two and four months, with the third dose at the child's first birthday. All three vaccines are given by intramuscular injection. About 5 percent of children may develop fever or soreness in the area of the injection.
Other preventive measures include isolating patients with respiratory hemophilus infections; treating appropriate contacts of infected patients with rifampin; maintaining careful standards of cleanliness in hospitals,
Bacteria—Singular, bacterium; tiny, one-celled forms of life that cause many diseases and infections.
Epiglottitis—Inflammation of the epiglottis, most often caused by a bacterial infection. The epiglottis is a piece of cartilage behind the tongue that closes the opening to the windpipe when a person swallows. An inflamed epiglottis can swell and close off the windpipe, thus causing the patient to suffocate. Also called supraglottitis.
Exudate—Cells, protein, fluid, or other materials that pass through cell or blood vessel walls. Exudates may accumulate in the surrounding tissue or may be discharged outside the body.
Intubation—A procedure in which a tube is inserted through the mouth and into the trachea to keep the airway open and to help a patient breathe.
Nosocomial infection—An infection acquired in a hospital setting.
Tracheotomy—An surgical procedure in which the surgeon cuts directly through the patient's neck into the windpipe below a blockage in order to keep the airway open.
See also Hib vaccine.
Daum, Robert S. "Haemophilus influenzae." In Nelson Textbook of Pediatrics. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.
St. Geme, Joseph W. "Haemophilus influenzae." In Principles and Practice of Pediatric Infectious Diseases, 2nd ed. Oxford, UK: Church Livingston, 2002.
Rebecca J. Frey, PhD Rosalyn Carson-DeWitt, MD